1. Technical Field
The present invention relates to a route retrieval apparatus and a navigation apparatus that calculate a fuel cost of each section (road section) based on road information contained in map data, and that retrieve a route with a lowest total of the fuel costs from a departure point and a destination point.
2. Description of Related Art
A known route retrieval apparatus calculates a fuel cost of each section based on road information contained in map data, and retrieves a route with a lowest total of the fuel costs from a departure point and a destination point. Such a route retrieval apparatus may correct a fuel cost by using gradient (road gradient) information of each section contained in the road information of the map data (see paragraphs [0026] to [0027] of JP-H5-189698A1 for example).
The inventor of the present application has found out the followings.
Since the gradient information contained in the road information is prescribed on a section-by-section basis (e.g., on a link-by-link basis), one section inclined at a constant gradient between both ends thereof and another section having up/down hills between both ends thereof are the same in the gradient indicated by the gradient information, as long the one section and the another section have the same height difference between the both ends. As a result, when the fuel cost is corrected by using the gradient information, the one section and the another section are the same in correction amount. However, in reality, when a vehicle travels on roads, the fuel consumption is less efficient in a section having up/down hills as compared with a wholly-flat section.
As can be seen from the above, the route retrieval apparatus is configured to calculate the fuel cost of each section based on the road information of the map data, correct the fuel cost of each section based on the gradient information of the each section contained in the road information, and retrieve a route with a lowest total of the fuel costs from a departure point to a destination point. In this configuration, since the route retrieval apparatus does not take into account the up/down hills in the course of a section, the route retrieval apparatus has low accuracy in retrieving a route with a lowest total of fuel costs.